Thermostat wiring question for Carrier Furnace and AC

DerekS · February 13, 2015, 05:12:58 PM

Hi,

I have:

Carrier 58MN7A Furnace (two stage)
Carrier 24ANB6 A/C (I think is single stage only based on only having three wires going to it)

I am wiring in a new thermostat and have a question about the wiring.

My question is for the A/C wiring in particular.

The MB in the Carrier Furnace has a connector for Y/Y2 and Y1
The MB in the Carrier A/C has a connector for only Y

Is it wrong to connect both the Y/Y2 and Y1 wires to the Thermostat?

Connecting the wire makes the system think I have dual stage cooling... but I wasn't sure if this is for fan control or something else and that I need to have a dual stage A/C unit for this.

Your help is greatly appreciated.

Thanks

D.

Admin · February 13, 2015, 07:07:08 PM

You probably have a Carrier 59MN7A furnace.

The AC is single stage so you would use only the Y/Y2 terminal in the furnace. Then depending on the size of the furnace and AC, adjust SW2 in the furnace for proper cooling airflow.

Using an Infinity controller is the best option.

DerekS · February 13, 2015, 08:55:10 PM

Thank you very much for your response,

Yes you are right.... it is a 59MN7A furnace (Typo on my part)

I did as you suggested and disconnected the Y1 wire from the thermostat.

In terms of the Dip Switches I currently have them set like this:

SW1-1 - OFF

SW1-2 - ON - To use a two stage thermostat using Min - Max heat

SW1-3 - OFF - Should I change this to ON since I have an Aprilair 600 Humidifier? Is this considered a By-Pass Humidifier?

SW1-4 - ON - Should I change this to OFF to put the furnace into Comfort mode rather than Economy mode? I care more about comfort than economy

SW1-5 - OFF - for 350 CFM

SW1-6 - OFF

SW1-7 - ON
SW1-8 - OFF (These set like this put the blower off delay to 120 seconds) Any recommendation for this?

SW2 - (All Off currently) - Any advice as to what these should be set to for optimal cooling?

SW3 - (All Off currently) - Any advice as to what these should be set for in terms of continuous fan operation?

SW4-2 - OFF - Turn it ON for Intermediate / Max heat using two stage thermostat
SW4-3 - OFF - For 350 CFM

1) Do you recommend the Min / Max staging or Intermediate / Max staging?
2) Any advice for the SW2 and SW3 settings?
3) Any advice to put the system to 400 CFM over the existing 350 CFM it is set for now?

Thanks!

D.

Admin · February 14, 2015, 08:38:01 AM

What's the full model of the furnace and AC? We would need to know the sizing of both in order to select the correct airflow settings.

DerekS · February 14, 2015, 09:25:29 AM

The full model number of the furnace is:

59MN7A060V171114

Full model number of the A/C is:

24ANB624A30010

What is the difference between Min-Max and Intermediate-Max staging?

The other question I have is in regards to the choice between Comfort or Economy Mode on a Carrier Furnace.

It says the difference between the two is that the airflow is reduced in the various stages for maximum comfort which seems sort of backwards to me.

Reduced airflow to me says the fan is running slower which would use less energy (would it not?)... how is reduced airflow a comfort mode? or am I reading this completely wrong?

D.

Admin · February 14, 2015, 03:51:53 PM

QuoteSW1-1 - OFF

GOOD

QuoteSW1-2 - ON - To use a two stage thermostat using Min - Max heat

ARE YOU USING A TWO STAGE HEATING THERMOSTAT AND WIRING BOTH W/W1 AND W2 TERMINALS? THIS IS IMPORTANT TO KNOW BECAUSE IF YOU ONLY HAVE A SINGLE STAGE HEATING THERMOSTAT THEN WE NEED TO TURN SW1-2 AND SW4-2 OFF.

QuoteSW1-3 - OFF - Should I change this to ON since I have an Aprilair 600 Humidifier? Is this considered a By-Pass Humidifier?

YES, THIS IS A BYPASS HUMIDFIER AND SW1-3 CAN BE TURNED ON.

QuoteSW1-4 - ON - Should I change this to OFF to put the furnace into Comfort mode rather than Economy mode? I care more about comfort than economy

THE IDEA IS THAT THE FURNACE WILL HAVE A HIGHER SUPPLY TEMPERATURE COMING FROM THE VENTS WHEN THE AIRFLOW IS REDUCED. THE RATING PLATE WILL HAVE A TEMPERATURE RISE RATING. TO INCREASE THE TEMPERATURE RISE YOU LOWER THE FAN SPEED. TO DECREASE THE TEMPERATURE RISE YOU RAISE THE FAN SPEED. YOU WANT TO ENSURE THE TEMPERATURE DIFFERENCE BETWEEN THE RETURN AIR DROP (UPSTREAM OF THE HUMIDIFIER BYPASS) AND SUPPLY PLENUM ARE WITHIN THE RANGE LISTED ON THE RATING PLATE. MAX IS 35F-65F, INTERMEDIATE IS 50F-80F AND MIN IS 35F-65F. IF SW1-4 IS ON THEN I BELIEVE THIS IS THE COMFORT MODE AND NOT THE EFFICIENCY MODE.

QuoteSW1-5 - OFF - for 350 CFM

I WOULD TURN THIS ON FOR 400CFM PER TON. ALSO LEAVE SW4-3 OFF.

QuoteSW1-6 - OFF

GOOD

QuoteSW1-7 - ON
SW1-8 - OFF (These set like this put the blower off delay to 120 seconds) Any recommendation for this?

TURNING SW1-7 and SW1-8 BOTH OFF WILL TURN THE BLOWER OFF AFTER 90 SECONDS AND ENSURE NO COOL AIR IS BEING BLOWN THROUGH THE DUCTS. MOST PEOPLE WILL RUN THIS TYPE OF FURNACE FAN CONTINUOUSLY, SO THE FAN SPEED WILL DROP BUT CONTINUE TO RUN AFTER A CALL FOR HEAT.

QuoteSW2 - (All Off currently) - Any advice as to what these should be set to for optimal cooling?

IF THE FURNACE IS A 060-14 (60,000 BTU's) AND THE AC IS A 24 (2 TON) THEN YOUR COOLING SPEED IS SET AT A DEFAULT 1200 CFM. THE RULE OF THUMB IS 400 CFM PER TON. TURN SW2-1 OFF, SW2-2 ON, SW2-3 OFF for 800 CFM, OR TURN SW2-1 ON, SW2-2 ON, SW2-3 OFF FOR 1000 CFM. EITHER SHOULD WORK FINE.

QuoteSW3 - (All Off currently) - Any advice as to what these should be set for in terms of continuous fan operation?

WITH AN ECM FAN MOTOR IT WON'T COST A FORTUNE TO RUN THE FAN CONTINUOUSLY. THIS WILL HELP ELIMINATE HOT AND COLD SPOTS AND IMPROVE THE FILTRATION OF YOUR AIR. LEAVE SW3-1, SW3-2, SW3-3 ALL OFF FOR THE LOWEST FAN SPEED. IF YOU TURNED SW1-5 ON FOR 400 CFM, THEN THE CONTINUOUS FAN SPEED WILL BE 600 CFM. THEN YOU SWITCH THE THERMOSTAT FAN FROM AUTO TO ON TO TAKE ADVANTAGE OF THE CONTINUOUS FAN.

QuoteSW4-2 - OFF - Turn it ON for Intermediate / Max heat using two stage thermostat

I CAN CLARIFY ONCE I KNOW WHAT KIND OF THERMOSTAT YOU ARE USING. YOU SHOULD BE USING A CARRIER INFINITY CONTROLLER TO TAKE ADVANTAGE OF BOTH YOUR FURNACE AND AC. LET ME GUESS YOU LIKE THE LOOK OF THE NEST THERMOSTAT?

QuoteSW4-3 - OFF - For 350 CFM

LEAVE SW4-3 OFF BUT TURN SW1-5 ON FOR 400 CFM PER TON OF COOLING.

Quote1) Do you recommend the Min / Max staging or Intermediate / Max staging?

I WOULD TRY MIN / MAX FIRST IF IN FACT YOU HAVE A TWO STAGE THERMOSTAT. IF YOU HAVE A SINGLE STAGE THERMOSTAT THEN LEAVE SW1-2 and SW4-2 OFF TO ALLOW THE FURNACE TO MODULATE IT'S OWN STAGES.

QuoteWhat is the difference between Min-Max and Intermediate-Max staging?

WITH A TWO STAGE THERMOSTAT THE FURNACE WILL FIRE IN MIN AND MAX OR INTERMEDIATE AND MAX. YOUR FURNACE HAS A MAX OUPUT OF 59,000 BTU'S, AN INTERMEDIATE OUTPUT OF 39,000 BTU'S AND A MIN OUTPUT OF 24,000 BTU'S.

QuoteThe other question I have is in regards to the choice between Comfort or Economy Mode on a Carrier Furnace.

It says the difference between the two is that the airflow is reduced in the various stages for maximum comfort which seems sort of backwards to me.

Reduced airflow to me says the fan is running slower which would use less energy (would it not?)... how is reduced airflow a comfort mode? or am I reading this completely wrong?

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

DerekS · February 14, 2015, 03:55:59 PM

I have a two stage Thermostat and I have wired W/W1 and W2 to the respective terminals in the Furnace

For cooling I have only wired Y1 on the Thermostat to Y/Y2 on the furnace and then to Y on the A/C unit (as it was pointed out I do not have two stage cooling)

(I also connected C and R to the outside A/C unit from the Furnace)

And yes... you caught me.... it's a NEST thermostat.

D.

Admin · February 14, 2015, 04:30:32 PM

I like the NEST thermostat. It's good looking and easy to setup and get working on a smart phone. I would switch to a NEST if it could control my humidifier and HRV. Right now I use a Honeywell Prestige V2.0.

In your case I would set SW1-2 ON and SW4-2 OFF to run MIN and MAX staging.

How many wires do you have at the thermostat?

RH
RC
Y
G
C
W1
W2
*

If you have 7 wires you can cheat and use only 1 wire on RH and install a jumper from RH to RC on the thermostat. Then you can wire * and control the humidifier as well. Just disconnect the wire you connect to * off the furnace control board and marette it with one of the humidifier wires, then connect the second humidifier wire to C on the furnace control board.

I recommend using the C connection on that thermostat if possible.

DerekS · February 14, 2015, 04:43:14 PM

I actually have 10 conductors running from the Thermostat to the Furnace (I did two runs of 5 conductor wire to make sure I had enough)

Here is what I have connected:

Thermostat - Furnace - AC
Y1 - Y/Y2 - Y
G - G
W1 - W/W1
W2/Aux - W2
C - COM 24V - C
Rh - R - R

* to the Humidifier Solenoid wire that was going to the HUM spade on the Furnace MB
Other wire from the Humidifier Solenoid to the COM terminal of the MB

(It is an Aprilair 600 so it is the water control solenoid to turn the water on/off)

According to the PRO install manual it says this about jumping Rc and Rh

QuoteNest's press connectors are built so that only one wire can be inserted per connector. Please don't put any jumper wires in Nest connectors. For example, Nest has an automatic internal jumper between the Rh and Rc wires. If both an Rh and Rc wire are put in their respective connectors, Nest will not jumper the connectors together. If the system has both heating and cooling and only one R wire, Nest will automatically jumper the connectors together.

Do you think it is better to take one of the spare wires and make a physical connection from Rc at the Thermostat and connect it to the R terminal in the Furnace?

D.

Admin · February 14, 2015, 04:55:01 PM

You have plenty of wires then. No need to jumper RC and RH at the thermostat. That's just a way to save a wire.

QuoteNest's press connectors are built so that only one wire can be inserted per connector. Please don't put any jumper wires in Nest connectors. For example, Nest has an automatic internal jumper between the Rh and Rc wires. If both an Rh and Rc wire are put in their respective connectors, Nest will not jumper the connectors together. If the system has both heating and cooling and only one R wire, Nest will automatically jumper the connectors together.

I did not know that. In that case you're all set

And yes you can remove the spade from the HUM terminal on the board and connect it to the wire you attached to * on the thermostat. The other humidifier wire can stay connected to C. The only problem I ran into was because of my fat fingers trying to setup the NEST to work with the humidifier. There's an option so that it's only powered with heating.

Because you're not using a communicating thermostat you don't need to wire R at the AC. Just wire C and Y and install a jumper between Y and R at the AC. But if you have the 3 wires to the AC already, then you can keep things connected the way they are. Most people would only have 2 wires going to their AC.

DerekS · February 14, 2015, 05:12:16 PM

Thanks for confirming not needing the extra wire.

I know the Humidifier setting you are talking about.

It walks you though what * is used for.

I chose Humidifier... it then prompts for:

Activate - choices are - Humidifier Only or Humidifier with Heat
Fan - Activate or do not activate

According to the manual it says that with a ByPass Humidifier it should be set to Humidifier with Heat and to Activate the Fan

This made sense to me as I figured it needed to activate the fan since if the fan wasn't running, what's the point of making water go over the humidifier.... it wouldn't get picked up by anything... and isn't the idea to add moisture to warm air? If not it will just pump out cold air through the vents.

D.